Actually I've just found a link to how to tweak the script so that you can enjoy DX10 graphics (provided you have a DX10 ready card) using XP with SP2. I'll have to go back to where I saw it, but the kids are literally just about to barge in from school, with friends in tow, so it's time I retired for a cat nap in preparation for tonights gaming fest and forum hopping. i'll post the link later I promis,.
As for your question, I run two NVida 8600GTS 256Mb cards in SLI on my main computer, but have just purchased one NVidia 8800GTS 640Mb card, which I haven't bothered to install yet (been too busy hospital hopping this week), but once I do the SLI set up will go onto my second games computer. (Thankfully when I built it in March I bought an SLI ready MoBo just in case) (says Phew!)
The two 8600GS cards together do allow me to play on hight settings using XP, but I have to keep anti-aliasing off, which is a pity as it does sharpen everything significantly, especially if you set it to x16. Unfortunately setting it on that caused serious lag when I was in a fire fight with several Koreans (my cpu is an Athlon 6000+ dual core {2 x 3GHz}) I'm hoping the 8800 card will allow me to play with everything maxed out.
I've yet to try the fix that will allow you to use the DX10 emulation.
When I do I'll post here to let you know the result. (probably next week as weekends are kid's days on the computer apart from my morning game review)
For a $100 card I doubt you can, but for $240 to $250 you should be able to buy two NVidia 8600GS 256Mb cards that will enable a reasonable frame rate.
The links BuBBy has provided are useful.
I'll be back. (the boys are here, lol)